Neutral Ramming Mass Material for Induction Furnace

An induction furnace consists of a non-conductive refractory crucible surrounded by a coil of copper tubing. Running a strong alternating current through the coil creates a magnetic field that induces an electric current inside the metal and rapidly melts the charge inside the furnace through the Ohmic effect. The coil is made of hollow copper tubes through which cooling water flows. The water absorbs heat from the bath through the refractory lining and is then recirculated through a heat exchanger. A proper and well-maintained refractory lining is very important for the safe operation of an induction furnace. The physical properties of electric induction require that the neutral lining of the induction furnace be as thin as possible. At the same time, it must be thick enough to adequately protect the coil from metal depletion due to corrosion and mechanical shock. Ensuring that the lining remains within the limits specified by the manufacturer requires careful use of the lining as well as an inspection and monitoring program during operation.

Neutral Ramming Mass for Induction Furnace

Refractory Ramming Mass for Neutral Lining of Induction Furnaces

Neutral linings for induction furnaces are usually made of acidic (silicon dioxide) or basic (magnesium oxide) compounds. It is very important to select the right refractory material for a given melting or holding application. The choice of refractory lining depends on many factors, such as melting temperature, holding time, volume, induction stirring, additives, alloying agents etc. Considering that magnesium oxide has poor thermal shock resistance and silica-based linings are rapidly corroded. Therefore, the new energy concept is neutral ramming mass (NRM). It mainly consists of Al2O3 with the addition of MgO in the matrix, which forms in-situ spinel (MgO·Al2O3) at the melting temperature of steel. The in-situ spinel formation is associated with a significant volume expansion and provides a rigid structure. It also provides a hard sintered refractory surface layer to the metal bath, resulting in good corrosion resistance. The inner refractory layer will remain powdery. If the hot face erodes, the next inner layer is exposed to a higher temperature and is sintered in turn by in-situ spinel formation.

Types of Refractory Ramming Materials and Technical Improvement Directions

Refractory ramming materials are divided into acidic, neutral, alkaline, carbon, etc. According to the material category, there are clay, high alumina, mullite, corundum, silicon, magnesium, silicon carbide, mullite corundum, etc. The binder is combined in different ways such as water glass, phosphoric acid, phosphate, aluminum sulfate, brine, high alumina cement, clay, etc.

Refractory ramming materials have good chemical stability, erosion resistance, wear resistance, and thermal shock resistance. Carbon materials are generally used in furnace bottoms with temperatures exceeding 1500℃, and can even be used at 2200℃. For example, this type of ramming material is used in the furnace bottoms of blast furnaces and calcium carbide furnaces.

Neutral ramming materials, such as high alumina and corundum ramming materials, are used for furnace linings in neutral atmospheres. Used to fill the gap between the furnace cooling equipment and the masonry for leveling.

Both alkaline and acidic ramming materials are used in medium frequency furnaces. If iron materials are to be smelted, acidic ramming mass is used. If steel materials are to be smelted, alkaline magnesium ramming mass is used. Some medium frequency furnace linings that smelt both iron and steel use magnesium ramming mass.

Acidic ramming mass is made of silica as raw material and can be used as filler for sulfuric acid tower. It can also be used in medium frequency furnace lining.

Refractory ramming mass has low moisture content and is rammed firmly, and its various properties are better than refractory castables. However, the disadvantage of ramming mass is that the construction speed is very slow and the labor intensity is high.

Refractory ramming mass does not have as many types as refractory castables, but the effect of using it in the iron ditch skimmer, branch ditch and residual ditch is indeed better than that of refractory castables. With the continuous evolution of the actual use of the market, ramming mass also has the direction of continuous technical improvement. For example, composite ramming mass is suitable for use in the case of complex furnace lining atmosphere.